Molding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. A mold is a hollowed out block that is filled with powder (which is subsequently melted) or a liquid. Rotational molding (rotomolding) involves heating a hollow mold which is filled with a charge or shot weight of material. It is then slowly rotated causing the softened material to disperse and stick to the walls of the mold. To maintain even thickness, the mold continues to rotate during the heating phase. The mold is then cooled and the part is removed from the mold. Rotational molding machines may be a rock and roll machine, a clamshell machine, a vertical or up and over rotational machine, a shuttle machine, a swing arm machine, or a carousel machine.
The materials used in a rotational mold may be from the polyethylene family such as: cross-linked polyethylene (PEX), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and regrind. Other compounds may be polyvinyl chloride (PVC) plastisols, nylons, polypropylene, nylon, polycarbonate. In addition to plastics, other materials may be used such as: acrylonitrile butadiene styrene (ABS), acetal, acrylic, epoxy, fluorocarbons, ionomer, polybutylene, polyester, polystyrene, polyurethane, silicone, or even various foods like chocolate.
Because rotomolding primarily uses gravity to push the material into the mold, the chosen material is typically in powder form with particle sizes of sufficient refinement to enter the detailed portions of the mold. At least one problem with fine particle sizes is dust which may enter motors or other machinery in the factory resulting in jams or other issues. Furthermore, the dust presents a potential hazard to employees in the factory. The fine particles may also go to waste if they disperse into the air when they are loaded into the mold resulting in raw material losses.
Prior systems for powder loading rely on volume which can be inaccurate. A vacuum device draws up the raw material from a reservoir into a hopper. The material is then dispensed gravimetrically and/or volumetrically through a valve in the bottom of the hopper.
It is at least one object of this invention to provide a novel method and system for loading of fine particles. Other advantages are apparent to one of skill in the art on reviewing the specification and figures as presented herein.